I keep wanting a “protected” access level, but I must also admit that there was
something really elegant about Swift 2’s access scheme (and I think most of us
feel like the word ‘fileprivate’ feels out of place). I was thinking about how
to mesh those two ideas, and I think I may have come up with a solution.
I propose we replace ‘fileprivate’ with a new ‘hidden’ access level. Hidden
would work exactly the same way as fileprivate does now, but adds the
connotation that what is hidden can also be unhidden. By adding ‘import hidden
TypeName’ to another file, that file also gains access to all of the hidden
items of that type (kind of like if it was in the same file).
#FileA
import Foundation
Struct A {
private var x:Int
hidden var y:Int //This is just like fileprivate, but can also
be shared with other files
}
extension A {
//y can be accessed here because they are in the same file
}
#FileB
import Foundation
import hidden A //This allows the entire file to see A’s hidden
variables
extension A {
//y can be accessed here because of the ‘import hidden’
declaration
}
#FileC
import Foundation
extension A {
//y can NOT be seen or accessed here because it is hidden
}
I think this is a fairly elegant solution to our protected dilemma, which also
feels in sync with Swift 2’s file-based scheme. The key features:
• Extensions no longer need to be piled in the same file if it is
getting too long
• Subclasses can be in their own file, but still have access to the
necessary parts of their superclass
• It communicates the author’s intent that the items are not meant to
be visible to its users, but that it is expected to be used for
extension/subclassing
• It requires an explicit statement ‘import hidden’ to access the
hidden variables. Safe by default, with override.
• It is not bound by module boundaries (i.e. you could use it for
subclassing classes from an imported module)
• Roughly the same length as ‘private’ and ‘public’ so various
declarations packed together are much easier to read (fileprivate breaks
reading rhythm)
Worth a formal proposal?
Thanks,
Jon
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